This invention relates to furnace systems for melting aluminum and particularly to an arrangement wherein gas-fired burners provide both convective and radiant heating of aluminum.
Aluminum melters currently in use are generally either electric furnaces or direct fuel-fired furnaces. An example of a known type of electric aluminum melting furnace is given in U.S. Pat. No. 3,996,412, which describes a furnace using silicon carbide electrical resistance elements to radiate energy to aluminum in a heating chamber.
Direct-fired furnaces have several disadvantages. Unless chemical fluxes are added regularly to the molten aluminum baths of such furnaces, the quality of metal produced is poor because air and the products of combustion react with molten aluminum, producing gases which dissolve in the aluminum and lead to voids or inclusions in castings produced from the aluminum. Fluxes improve metal quality, but give off corrosive vapors which are an environmental hazard and may also render impractical the use of recuperators or other heat-saving devices. Direct-fired furnaces also require frequent cleaning and suffer from excessive formation of dross, resulting in metal losses of up to three to five percent.
Electrically heated aluminum melters avoid many of the above-described problems. Since they transfer heat to aluminum through radiation alone, the metal produced is clean. However, their electrical heating elements typically are quite fragile and have short lives. Also, high melting rates may be difficult to achieve in electric furnaces, and temperature recovery of their bath following input of a cold charge may be slow.
Accordingly, it is an object of the invention to provide an improved aluminum melter.
It is an object of the invention to provide an aluminum melting system which produces high quality aluminum with low metal losses and which has relatively low maintenance requirements.
It is also an object of the invention to provide an aluminum melting system wherein heat transfer is effected by both convection and radiation.
It is a further object of the invention to provide a method and apparatus for melting aluminum wherein convection and radiation heating are performed in separate sections of a melting system.